Ignition system for an internal combustion engine

ABSTRACT

In an ignition system, a plurality of parallel circuits each of which comprises a switching element, a capacitor and a primary winding of an ignition coil are connected in series, and a plurality of switching element controlling means are respectively connected to said switching element, whereby abnormal firing is prevented.

United States Patent Nagasawa Oct. 14, 1975 [54] IGNITION SYSTEM FOR AN INTERNAL 3,587,550 6/1971 ZfiChlin 123/148 MC CONIBUSTION ENGINE 3,704,397 1 H1972 Crouch et 81.... 123/148 MC 3,723,809 3/1971 Fujii 123/148 MC [75] Inventor: Masao Nagasawa, a y p 3,741,185 6/1973 Swifi 61311.... 123/148 MC Assignee, Nippondenso Co Ltd Kariya 3,809,044 5/1974 Jereb et a1. 123/148 MC Japan Przmary Exammer-Wendell E. Burns Filedl y 1974 Assistant Examiner-James Winthrop Cranson, Jr. [2]] App], 475 279 Attorney, Agent, or FirmCushman, Darby &

Cushman [30] Foreign Applicatlon Priority Data [57] ABSTRACT July 10, 1973 Japan, 48-78058 In an ignition System, a plurality of parallel circuits 52] U S Cl 123/148 R each of which comprises a switching element, a capac- [51] F02G 1/00 itor and a p y winding of an ignition coil are com [58] Field of Search 23/148 MC nected in series, and a plurality of switching element controlling means are respectively connected to said References Cited switching element, whereby abnormal firing is pret (1. UNITED STATES PATENTS 8 3,577,971 5/1971 Cavil 123/148 MC 9 m 10 Draw'ng Flgures v US. Patent Oct. 14, 1975 Sheet 2 of5 3,911,886

F/G.Z-A

US. Patent Oct-14', 1975 Sheet 3 of5 3,911,886

FIG.3

0ne revolution of d crank shaft (A A m A J if J (B) A A A J A v v v v v v v L v AJ\ A A AA A v c TIV TZY Ts T4! T5 TGY, 'IF'IYF; lt IV Tzv Formdl A Reverse A A (E) V v d I/ I-E-I l (F) V V US. Patent Oct. 14, 1975 Sheet 4 of5 3,911,886

U.S. Patent O ct. 14, 1975 Sheet 5 of5 3,911,886

IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an ignition system in which a magneto generator is employed an electric power source, and especially to a capacitor discharge type contactless ignition system for providing ignition sparks successively to respective spark plugs of a multicylinder engine.

2. Description of Prior Art In a conventional well-known ignition system of this kind, there are provided one alternating current generating coil, one capacitor connected to the generating coil and a plurality of thyristors connected in parallel with the capacitor, and each of the thyristors is made conductive, one by one, in order to discharge the charge stored in the capacitor, whereby each cylinder is supplied in order with an ignition spark due to the discharge. However in such a conventional ignition system, while the charge on the capacitor is discharged through a circuit comprising the capacitor, a thyristor and a primary winding of an ignition coil, another thyristor may be made conductive due to an induced noise voltage of said ignition coil, whereby an abnormal firing may be caused at a cylinder which is not at an ignition timing.

In another conventional ignition system, in which there are provided one alternating current generating coil, a plurality of capacitor and a plurality of thyristors respectively connected in parallel with the capacitors, an abnormal firing may be also caused in a like manner described before.

SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide an ignition system which prevents such an abnormal firing during the normal running of an engine.

It is another object of the present invention to provide an improved ignition system which exhibits good ignition timing advancing characteristic by providing a transformer or the like.

It is a further object of the present invention to provide an improved ignition system which can prevent an ignition spark from being produced during the reverse rotation of the engine, whereby the engine can be prevented from continuing to rotate in the reverse direction by itself.

The above and further objects and novel features of the present invention will be more fully apparent from the following detailed description when the same is read in connection with the accompanying drawings.

It is to be expressly understood, however, that each drawing is for purpose of illustration only and is not intended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric wiring diagram showing the first embodiment of the present invention,

FIG. 2(A) is a longitudinal sectional view of a magneto generator employed in the present invention, which is taken along the line IIA-IIA in FIG. 2(B),

FIG. 2(8) is a transverse sectional view of the magneto generator taken along the line IIB-IIB in FIG. (A).

FIG. 3 is a waveform diagram for explaining mainly the operation of the first embodiment,

FIG. 4 is an electric wiring diagram showing the second embodiment of the present invention,

FIG. 5 is an electric wiring diagram showing the third embodiment of the present invention,

FIG. 6 is a partial electric wiring diagram which can be a replacement for part of the second embodiment (FIG. 4), and

FIGS. 7, 8 and 9 are partial electric wiring diagrams which can be replacements for part of the third embodiment (FIG. 5).

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to FIG. 1 showing the first embodiment of the present invention, numeral 1 designates a high speed capacitor charging coil having a relatively low number of turns for generating a larger electric power during high speed running of an engine, numeral 2 designates a low speed capacitor charging coil having a relatively high number of turns for generating a larger electric power during mainly a low speed running of the engine. A numeral 3 designates a diode for rectifying alternating current generated at said coils 1 and 2, 4 and 5 capacitors, 6 and 7 ignition coils having primary windings 6a and 7a and secondary windings 6b and 7b, 8 and 9 diodes connected in parallel with said primary windings 6a and 7a for extending arc duration of ignition sparks produced at spark plugs 14 and 15, 10 and 11 thyristors constituting semi-conductor switching elements, 12 and 13 timing signal generating coils constituting timing signal generators mounted in a magneto generator, 16 and 17 diodes connected in parallel with said generating coils 12 and 13, and 16a a diode connected in parallel with said low speed capacitor charging coil 2.

Next the construction of the magneto generator which can be employed in the ignition system according to the present invention will be explained with reference to FIGS. 2(A) and 2(B). A numeral 30 designates a rotor comprising an iron shell 31, eight permanent magnets 32a to 32/1 spaced apart at equal intervals and securely embedded in the inner side of the iron shell 31 by means of a nonmagnetic material 31a such as aluminum or resin, pole pieces 33a to 3311 secured respectively to the inner face of the permanent magnets 32a to 32/1, a center piece 34 securely mounted on a crankshaft 34a of an engine by a nut 34b and securely fixing the iron shell 31 by means of rivets (not shown) and timing cores 35a to 35g secured to the center piece 34. A numeral 40 designates a stator secured to the engine, 41 and 42 capacitor charging cores securely mounted on the stator 40 at a position opposite to each other and on which said high speed and low speed capacitor charging coils 1 and 2 are wound. Numerals 43a and 43b designate lamp load cores securely mounted on the stator 40 at a position displaced respectively by about from said capacitor charging cores 41 and 42, with a lamp load supply coils 44a and 44b constituting a power supply for a load such as lamps. Numerals 22a and 22b designate stators of said timing signal generators securely mounted on the stator 40 at a position angularly displaced respectively by With the magneto generator constructed above described, for each revolution of the magneto generator i.e., for each rotation of the engine crankshaft 34a, the capacitor charging coils 1 and 2 generate four cycles of the AC no-load voltage as shown by solid line in FIG. 3(A), while, for each rotation of the crankshaft 34a, the timing signal generating coils l3 and 12 of the timing signal generators respectively generate seven cycles of the no-load output voltage as shown in FIGS. 3(8) and (C). l

The operation of the first embodiment constructed as described above will now be explained with reference to FIG. 1 to FIG. 3. The operation of the various parts of the embodiment which take place along with the rotation of the engine will be explained with reference to FIG. 3 showing the waveforms produced at various points of the system. When the generated voltage of the capacitor charging coils l and 2 begins to increase in the positive direction at a time T1 in FIG. 3, the thyristor 10 is made conductive by the output voltage produced at the timing signal generating coil 12 as shown in FIG. 3(C) and then the current due to the solid line voltage signal shown in FIG. 3(A) flows through the circuit comprising the capacitor charging coils 2 and l, the diode 3, the thyristor 10, the capacitor 5, a parallel circuit of the diode 9 and the primary winding 7a of the ignition coil 7, and the ground. This current charges the capacitor 5 to develop thereacross the terminal voltage as indicated by a broken line in FIG. 3(A). Thereafter, as the generated voltage of the capacitor charging coils I and 2 begins to increase in the negative direction at a time T2, the timing signal generating coils 12 and 13 generate the output voltages as shown in FIGS. 3(C) and (B) so that the thyristors and 11 are driven into conduction, whereby the charge stored in the capacitor 5 is discharged through the circuit comprising the capacitor 5, the thyristor 11, and the primary winding 7a of the ignition coil 7, thereby inducing a high voltage in the secondary winding 7b of the ignition coil 7 and producing an ignition spark at the spark plug 15.

Here, the thyristor 10 is driven into conduction at the same time, however, no ignition spark can be produced at the spark plug 14 since the capacitor 4 has not been charged.

When the second cycle of the generated voltage of the capacitor charging coils l and 2 begins to increase FIG. 3(A). in the positive direction at a time T3, the output voltages of the timing signal generating coils 12 and 13 make the thyristors 10 and 11 conductive and thus the capacitor charging coils 1 and 2 are shortcircuited' through the thyristors l0 and 11 to thereby make the charging of the capacitor, 4 or 5 ineffective as indicated by the broken line in FIG.3(A). And thereaf-' ter as the second cycle of the generated voltage begins to increase in the negative direction at a time T4, the timing signal generating coils 12 and 13 generate the output voltages, however no ignition spark can be produced at the spark plugs 14 and. 15 since the capacitors 4 and 5 have not been charged.

When the third .cycle of the generated voltage of the capacitor charging coils 1 and 2 begins to increase in the positive direction at a time T5, the thyristor 11 is made conductive by the output voltage produced at the timing signal generating coil 13 as shown in FIG. 3(8) and then the current flows through the circuit comprising the capacitor charging coils l and 2, the diode 3, the capacitor 4, a parallel circuit of the diode 8 and the primary winding 6a of the ignition coil 6, the thyristor 11 and the ground. This current charges the capacitor 4 to develop thereacross the terminal voltage as indicated by an one-dot-chain line in FIG. 3(A). Thereafter, as the third cycle begins to increase in the negative direction at a time T6, the timing signal generating coils l2 and 13 generate the output voltages, so that the thyristor 10 is driven into conduction, whereby the charge stored in the capacitor 4 is discharged through the circuit comprising the capacitor 4, the thyristor 10, and the primary winding 6a of the ignition coil 6, thereby inducing a high voltage in the secondary winding 6b of the ignition coil 6 and producing an ignition spark at the spark plug 14.

Here, in the like manner described before, the thyristor 11 is driven into conduction at the same time, however, no ignition spark can be produced at the spark plug 15 since the capacitor 5 has not been charged.

And further thereafter, at a time T7 both thyristors l0 and l l are driven into conduction due to the output voltages of the timing signal generating coils l2 and 13, and thus the capacitor charging coils l and 2 are shortcircuited through said both thyristors, thereby to make the charging of the capacitor 4 or 5 ineffective. And at a time T8 though both thyristors are made conductive no ignition spark can be produced at the spark plugs 14 and 15 in the like manner described before.

Consequently, the above-described process of the operation is repeated to alternatively produce an ignition spark at the spark plugs 14 and 15 for each rotation of the engine.

When the engine is forced to rotate in a reverse direction by accident, for instance, when a motor vehicle using the ignition system of the present invention moves down hill backwardly on a sloping road, the polarity of both the generated voltage of capacitor charging coils and the output voltages of the timing signal generating coils is reversed. Accordingly the generated voltage of the capacitor charging coils l and 2 begins to increase in the positive direction at times T8, T6, T4 and T2 and at every one of those times T8, T6, T4 and T2 both timing signal generating coils l2 and 13 generate the output voltages so that both thyristors l0 and l l are driven into conduction at the same time, whereby neither the capacitor 4 nor the capacitor 5 can be charged at any time thus preventing an ignition spark from being produced during the reverse rotation of the engine, and therefore the reverse rotation can not be continued by the engine itself.

The embodiment described above is designed for preventing the engine from being rotated in the reverse direction, however when there is no need to design the magneto generator for preventing the reverse rotation of the engine, some of the output voltages of the timing signal generating coils 12 and 13 can be eliminated, in other words, some of the seven cores 35a to 35g can be eliminated. In this respect, two cores of them, for instance, 35a and 35f are sufficient to get such output voltages as shown in FIGS. 2(D) and (E). According to this modification, when the thyristor is made conductive at the times T1 and T3 due to the output voltages of the coil 12 as shown in FIG. 2(D), the first and second cycle of the generated voltage of the capacitor charging coils l and 2 charges the capacitor 5 to develop thereacross the terminal voltage as indicated by a broken line in FIG. 2(F). At the time T5 the thyristor 11 is driven into conduction due to the output voltage of the coil 13 as shown in FIG. 2(E), and the charge stored in the capacitor 5 is discharged to produce an ignition spark 15, at the same time the capacitor 4 begins to be charged. Thereafter at the time T7, the capacitor 4 is going to be charged further as indicated by an one-dot-chain line in FIG. 2(F), and then at the time T1 whenthe thyristor 10 is made conductive, the capacitor 5 begins to be charged as well as the charge stored in the capacitor 4 is discharged to produce an ignition spark at the spark plug 14.

FIG. 4 illustrates the second embodiment of the present invention. The second embodiment differs from the first embodiment in that a series circuit of a diode 18 and a primary winding 21a of a transformer 21 having two secondary windings 21b and 21c is connected in parallel with capacitor charging coils l and 2, each one end of the secondary windings 21b and 21c is respectively connected to the gates of the thyristors 11 and 10 through respective diodes and 19, and diodes 16 and 17 are respectively connected in series between the gates of the thyristors 10 and 11 and the timing signal generating coils 12 and 13. According to this second embodiment, when the generated voltage of the capacitor charging coils 1 and 2 begins to increase in the negative direction, at the times T2, T4, T6 and T8 in FIG. 3 showing the waveforms of the magneto generator having the construction shown in FIG. 2, the secondary windings 21b and 21c of the transformer 21 generate output voltages due to electric current flowing through the primary winding 21a caused by the generated voltage increasing in the negative direction, so that the thyristors 10 and 11 are driven into conduction. During the low speed running of the engine, the output voltages of the secondary windings 21b and 21c of the transformer are not large enough to make the thyristors 10 and lll conductive before the thyristors 10 and 11 are driven into conduction due to the output voltages produced at the timing signal generating coils 12 and 13, however as the engine speed increases the output voltages of the secondary windings 21b and 21c increase large enough to make the thyristors conductive earlier than the output voltages of the timing signal generating coils 12 and 13. Therefore, at the time T2, when the ignition spark should be produced at the spark plug 15, the ignition timing can be advanced due to the output voltage of the secondary winding 21b, and in the same way at the time T6, the ignition timing when the ignition spark should be produced at the spark plug 14 can be advanced due to the output voltage of the secondary winding 210.

Here, at the times T4 and T8, the thyristors l0 and 11 are driven into conduction earlier than the conduction due to the output voltages of the timing signal generating coils l2 and 13 as well, however no problem occurs since the capacitors 4 and 5 have not been charged at those times as described before.

FIG. 5 illustrates the third embodiment of the present invention The third embodiment differs from the first embodiment in that a thyristor 25 is connected in parallel with the series circuit of the thyristors 10 and 11, a primary winding 21a of a transformer 21 having a secondary winding connected to the gate of said thyristor 25 is connected in parallel with the capacitor charging coils 1 and 2, and diodes 8a and 9a are respectively connected in parallel with the series circuits of the capacitors 4 and 5 and the primary windings 6a and 7a of the ignition coils 6 and 7. According to this third embodiment, the ignition timing can be advanced in the like manner as described in the second embodiment, however it should be noted in this embodiment that when the thyristor 25 is driven into conduction earlier than the thryristors l0 and 11, the charge stored in the capacitor 4 or 5 is discharged through the circuit comprising the capacitor 4, the thyristor 25, the ground, the diode 9a, and the primary winding 6a of the ignition coil 6, or the circuit comprising the capacitor 5, the diode 8a, the thyristor 25, the ground, and the primary winding 7a of the ignition coil 7. Other operation is almost same as that of the first embodiment.

FIG. 6 illustrates an arrangement of the transformer 21 shown in FIG. 4, in which a numeral 56 designates a voltage converting circuit comprising a zener diode 57 and two resistors 58 and 59 respectively connected to the gates of the thyristors 10 and 11, and the operation of this arrangement is almost same as that of the second embodiment.

FIGS. 7, 8 and 9 illustrate other arrangements which can be substituted for the transformer 21 shown in FIG. 5, and the operation is almost same as that of the third embodiment, whereby it is omitted.

In FIG. 7, a voltage converting circuit 26 operates as follows. When the generated voltage of the capacitor charging coils l and 2 increases in the negative direction, an electric current flowing through the ground, a resistor 26a, a capacitor 26b, and the diode 18 charges the capacitor 26b as indicated by its polarity. And thereafter as the generated voltage in the negative direction exceeds a predetermined value a zener diode 26c becomes conductive and then the generated voltage of the capacitor charging coils 1 and 2 is applied to a gate of a thyristor 26d so as to make it conductive, so that the charge stored in the capacitor 26b is discharged through the gate of the thyristor 25, the cathode thereof, the ground and the thyristor 26d, whereby the thyristor 25 is driven into conduction.

In FIG. 8, the end of the capacitor charging coil 2 is grounded through the gate and cathode of the thyristor 25 as well as a diode 16b in parallel. And a junction point of the capacitor charging coils l and 2 is also grounded through a series circuit of a resistor 55 and the diode 16a.

In FIG. 9, the thyristor 25 is replaced by a bidirectional thyristor 25a, and its gate is connected to a junction point of the capacitor charging coils l and 2 through a resistor 55 and the diode 16a.

What we claim is:

1. An ignition system for an internal combustion engine comprising;

a capacitor charging coil for generating an AC voltage;

a rectifying element, connected to said capacitor charging coil, for rectifying said AC voltage;

a capacitor connected to said capacitor charging coil through said rectifying element;

a switching element having a control gate and connected to said capacitor charging coil in parallel with said capacitor;

an ignition coil having a primary winding connected in series with said capacitor and a secondary winding;

a spark plug connected to said secondary winding of said ignition coil; and

a switching element controlling means connected to said control gate of said switching element; wherein the improvement comprises;

another capacitor connected to said capacitor charging coil through the parallel circuit of said switching element and said capacitor;

another ignition coil having a primary winding connected in series with said another capacitor and a secondary winding;

another spark plug connected to said secondary winding of said another ignition coil;

another switching element, having a control gate, and connected to said capacitor charging coil through said parallel circuit and in parallel with said another capacitor; and

another switching element controlling means connected to said gate of said another switching element, said switching element controlling means being so arranged to make said switching element conductive at least when said another capacitor is to be charged and when the charge stored in said capacitor is to be discharged at the ignition timing for said spark plug, and said another switching element controlling means being so arranged to make said another switching element conductive at least when said capacitor is to be charged and the charge stored in said another capacitor is to be discharged at the other ignition timing for said another spark plug,

each of said switching element controlling means and said another switching element controlling means respectively comprising a generating coil which generates an output voltage in synchronism with the rotation of said internal combustion engine.

2. An ignition system for an internal combustion engine in accordance with claim 1 further comprising;

a third switching element controlling means having two output terminals respectively connected to said gates of said switching element and said another switching element.

3. An ignition system for an internal combustion engine in accordance with claim 1 further comprising;

a third switching element having a control gate and connected to said capacitor charging coil through said rectifying element in parallel with both said switching element and said another switching element; and

a third switching element controlling means whose output terminal is connected to said control gate of said third switching element.

4. An ignition system for an internal combustion engine in accordance with claim 2, wherein said third switching element controlling means comprises a transformer having a primary winding connected in parallel with said capacitor charging coil.

5. An ignition system for an internal combustion engine in accordance with claim 2, wherein said third switching element controlling means comprises a zener diode whose anode is connected to said capacitor charging coil in parallel with said rectifying element, and whose cathode is connected in parallel to two resistors constituting said output terminals.

6. An ignition system for an internal combustion engine in accordance with claim 3, wherein said third switching element controlling means comprises a transformer whose primary winding is connected in parallel with said capacitor charging coil, and whose secondary winding constitutes said output terminal.

7. An ignition system for an internal combustion engine in accordance with claim 4, wherein said transformer comprises two secondary windings, each one end of which constitutes said output terminals.

8. An ignition system for an internal combustion engine comprising:

a series connection including a capacitor charging coil, a rectifying element, a first capacitor, a first primary winding, a second capacitor and a second primary winding;

a first discharge circuit including said first capacitor,

said first primary winding and a first switching element;

a first ignition coil having said first primary winding and a first secondary winding;

a first spark plug connected with said first secondary winding;

a first signal generator connected with said first switching element for generating a first ignitional signal, whereby the charge stored in said first ca pacitor is discharged to thereby produce the igni tion spark atsaid first spark plug;

a second discharge circuit including said second capacitor, said second primary winding and a second switching element;

a second ignition coil having said second primary winding and a second secondary winding;

a second spark plug connected with said second secondary winding; and

a second signal generator connected with said second switching element for generating a second ignition signal at a time except when said first ignition signal is generated, whereby the charge stored in said second capacitor is discharged thereby to produce the ignition spark at said second spark plug.

9. An ignition system for an internal combustion engine comprising:

a first charging circuit in series including a capacitor charging coil, a first capacitor and a second switching element, said first capacitor being charged with the output voltage at said capacitor charging coil when said second switching element is conductive;

a first discharging circuit in series including said first capacitor, a first switching element and a first primary winding, the charge stored in said first capacitor being discharged when said first switching element is made conductive;

a first ignition coil having said first primary winding and a first secondary winding;

a first spark plug connected with said first secondary winding;

a first signal generator connected with said first switching element for generating a first ignition signal thereby to make said first switching element conductive;

a second charging circuit in series including said capacitor charging coil, said first switching element and a second capacitor, said second capacitor a second signal generator connected with said second switching element for generating a second ignition signal thereby to make said second switching element conductive;

said first and second signal generator generating alternately said first and second ignition signal, whereby the charge and discharge for said first and second capacitor are alternately carried out, thereby producing ignition sparks alternately at said first and second spark plug. 

1. An ignition system for an internal combustion engine comprising; a capacitor charging coil for generating an AC voltage; a rectifying element, connected to said capacitor charging coil, for rectifying said AC voltage; a capacitor connected to said capacitor charging coil through said rectifying element; a switching element having a control gate and connected to said capacitor charging coil in parallel with said capacitor; an ignition coil having a primary winding connected in series with said capacitor and a secondary winding; a spark plug connected to said secondary winding of said ignition coil; and a switching element controlling means connected to said control gate of said switching element; wherein the improvement comprises; another capacitor connected to said capacitor charging coil through the parallel circuit of said switching element and said capacitor; another ignition coil having a primary winding connected in series with said another capacitor and a secondary winding; another spark plug connected to said secondary winding of said another ignition coil; another switching element, having a control gate, and connected to said capacitor charging coil through said parallel circuit and in parallel with said another capacitor; and another switching element controlling means connected to said gate of said another switching element, said switching element controlling means being so arranged to make said switching element conductive at least when said another capacitor is to be charged and when the charge stored in said capacitor is to be discharged at the ignition timing for said spark plug, and said another switching element controlling means being so arranged to make said another switching element conductive at least when said capacitor is to be charged and the charge stored in said another capacitor is to be discharged at the other ignition timing for said another spark plug, each of said switching element controlling means and said another switching element controlling means respectively comprising a generating coil which generates an output voltage in synchronism with the rotation of said internal combustion engine.
 2. An ignition system for an internal combustion engine in accordance with claim 1 further comprising; a third switching element controlling means having two output terminals respectively connected to said gates of said switching element and said another switching element.
 3. An ignition system for an internal combustion engine in accordance with claim 1 further comprising; a third switching element having a control gate and connected to said capacitor charging coil through said rectifying element in parallel with both said switching element and said anOther switching element; and a third switching element controlling means whose output terminal is connected to said control gate of said third switching element.
 4. An ignition system for an internal combustion engine in accordance with claim 2, wherein said third switching element controlling means comprises a transformer having a primary winding connected in parallel with said capacitor charging coil.
 5. An ignition system for an internal combustion engine in accordance with claim 2, wherein said third switching element controlling means comprises a zener diode whose anode is connected to said capacitor charging coil in parallel with said rectifying element, and whose cathode is connected in parallel to two resistors constituting said output terminals.
 6. An ignition system for an internal combustion engine in accordance with claim 3, wherein said third switching element controlling means comprises a transformer whose primary winding is connected in parallel with said capacitor charging coil, and whose secondary winding constitutes said output terminal.
 7. An ignition system for an internal combustion engine in accordance with claim 4, wherein said transformer comprises two secondary windings, each one end of which constitutes said output terminals.
 8. An ignition system for an internal combustion engine comprising: a series connection including a capacitor charging coil, a rectifying element, a first capacitor, a first primary winding, a second capacitor and a second primary winding; a first discharge circuit including said first capacitor, said first primary winding and a first switching element; a first ignition coil having said first primary winding and a first secondary winding; a first spark plug connected with said first secondary winding; a first signal generator connected with said first switching element for generating a first ignitional signal, whereby the charge stored in said first capacitor is discharged to thereby produce the ignition spark at said first spark plug; a second discharge circuit including said second capacitor, said second primary winding and a second switching element; a second ignition coil having said second primary winding and a second secondary winding; a second spark plug connected with said second secondary winding; and a second signal generator connected with said second switching element for generating a second ignition signal at a time except when said first ignition signal is generated, whereby the charge stored in said second capacitor is discharged thereby to produce the ignition spark at said second spark plug.
 9. An ignition system for an internal combustion engine comprising: a first charging circuit in series including a capacitor charging coil, a first capacitor and a second switching element, said first capacitor being charged with the output voltage at said capacitor charging coil when said second switching element is conductive; a first discharging circuit in series including said first capacitor, a first switching element and a first primary winding, the charge stored in said first capacitor being discharged when said first switching element is made conductive; a first ignition coil having said first primary winding and a first secondary winding; a first spark plug connected with said first secondary winding; a first signal generator connected with said first switching element for generating a first ignition signal thereby to make said first switching element conductive; a second charging circuit in series including said capacitor charging coil, said first switching element and a second capacitor, said second capacitor being charged with the output voltage at said capacitor charging coil when said first switching element is conductive; a second discharging circuit in series including said second capacitor, said second switching element and a second primary winding, the charge stored in said second capacitor being dIscharged when said second switching element is made conductive; a second ignition coil having said second primary winding and a second secondary winding; a second spark plug connected with said second secondary winding; and a second signal generator connected with said second switching element for generating a second ignition signal thereby to make said second switching element conductive; said first and second signal generator generating alternately said first and second ignition signal, whereby the charge and discharge for said first and second capacitor are alternately carried out, thereby producing ignition sparks alternately at said first and second spark plug. 